The role of mast cell-derived histamine in the closure of an in vitro wound

Mast cells and ocular surface: An update review

Mast cells (MCs), traditionally viewed as key players in IgE-mediated allergic responses, are increasingly recognized for their versatile roles. Situated at critical barrier sites such as the ocular surface, these sentinel cells participate in a broad array of physiological and pathological processes. This review presents a comprehensive update on the immune pathophysiology of MCs, with a particular focus on the mechanisms underlying innate immunity. It highlights their roles at the ocular surface, emphasizing their participation in allergic reactions, maintenance of corneal homeostasis, neovascularization, wound healing, and immune responses in corneal grafts. The review also explores the potential of MCs as therapeutic targets, given their significant contributions to disease pathogenesis and their capacity to modulate immunity. Through a thorough examination of current literature, we aim to elucidate the immune pathophysiology and multifaceted roles of MCs in ocular surface health and disease, suggesting directions for future research and therapeutic innovation.

Bioactive nanomaterials kickstart early repair processes and potentiate temporally modulated healing of healthy and diabetic wounds

Slow-healing and chronic wounds represent a major global economic and medical burden, and there is significant unmet need for novel therapies which act to both accelerate wound closure and enhance biomechanical recovery of the skin. Here, we report a new approach in which bioactives that augment early stages of wound healing can kickstart and engender effective wound closure in healthy and diabetic, obese animals, and set the stage for subsequent tissue repair processes. We demonstrate that a nanomaterial dressing made of silk fibroin and gold nanorods (GNR) stimulates a pro-neutrophilic, innate immune, and controlled inflammatory wound transcriptomic response. Further, Silk-GNR, lasered into the wound bed, in combination with exogeneous histamine, accelerates early-stage processes in tissue repair leading to effective wound closure. Silk-GNR and histamine enhanced biomechanical recovery of skin, increased transient neoangiogenesis, myofibroblast activation, epithelial-to-mesenchymal transition (EMT) of keratinocytes and a pro-resolving neutrophilic immune response, which are hitherto unknown activities for these bioactives. Predictive and temporally coordinated delivery of growth factor nanoparticles that modulate later stages of tissue repair further accelerated wound closure in healthy and diabetic, obese animals. Our approach of kickstarting healing by delivering the "right bioactive at the right time" stimulates a multifactorial, pro-reparative response by augmenting endogenous healing and immunoregulatory mechanisms and highlights new targets to promote tissue repair.

The effects of kiwifruit dressing on hypertrophic scars in a rabbit ear model

AIMS

Hypertrophic scars show abnormal responses during healing. These scars, associated with dysregulated growth and excessive collagen formation, can have both functional and cosmetic consequences for patients. The present study evaluated the effects of kiwifruit on hypertrophic scars in a rabbit ear model.

METHODS

This study included 13 New Zealand albino rabbits with full thickness wounds down to the cartilage (four wounds per ear; total: 104 scars). Sixteen days after initial wound formation, one ear of each rabbit was treated with daily kiwifruit dressing, while the other ear (control group) was dressed after normal saline irrigation for 10 days. Harvested skin samples were examined for histopathological, morphometric and immunohistochemical results.

RESULTS

In comparison with the control group, early kiwifruit dressing significantly reduced the scar elevation index, fibroblast count and dermal collagen organisation. The ratio of collagen type III to total collagen immunoreactivity, inflammation and dermal capillary count increased significantly in the treated group, compared to the untreated controls.

CONCLUSION

Based on the findings, early kiwifruit dressing improved the histological features of cutaneous wounds in rabbits. Therefore, this approach may be effective in clinical practice.

Management of keloid scars: noninvasive and invasive treatments

Scars vary from mature linear scars to abnormal excessive scars such as hypertrophic scars and keloid scars. Keloid scars are fibro-proliferative disease entities that reflect an abnormal process of wound healing. They can cause pain, itching, stiffness, and psychological distress, all of which can affect quality of life. Various treatment options have been advocated as ways to prevent and treat keloid scars. These include noninvasive treatments such as use of silicone gel sheeting and compression therapy, and invasive treatments such as intralesional corticosteroid injections, surgery, and radiotherapy. Novel treatments include chemotherapy, immunotherapy, and anti-inflammatory therapies. Unfortunately, keloids continue to pose a significant challenge due to the lack of efficacious treatments. Therefore, clinicians should be familiar with various therapeutic options and apply the most suitable treatment plan for patients. In this review, we introduce the current therapeutic options for the management of keloid scars.

A Review of the Evidence for and against a Role for Mast Cells in Cutaneous Scarring and Fibrosis

Scars are generated in mature skin as a result of the normal repair process, but the replacement of normal tissue with scar tissue can lead to biomechanical and functional deficiencies in the skin as well as psychological and social issues for patients that negatively affect quality of life. Abnormal scars, such as hypertrophic scars and keloids, and cutaneous fibrosis that develops in diseases such as systemic sclerosis and graft-versus-host disease can be even more challenging for patients. There is a large body of literature suggesting that inflammation promotes the deposition of scar tissue by fibroblasts. Mast cells represent one inflammatory cell type in particular that has been implicated in skin scarring and fibrosis. Most published studies in this area support a pro-fibrotic role for mast cells in the skin, as many mast cell-derived mediators stimulate fibroblast activity and studies generally indicate higher numbers of mast cells and/or mast cell activation in scars and fibrotic skin. However, some studies in mast cell-deficient mice have suggested that these cells may not play a critical role in cutaneous scarring/fibrosis. Here, we will review the data for and against mast cells as key regulators of skin fibrosis and discuss scientific gaps in the field.

Keloids and Hypertrophic Scars: Pathophysiology, Classification, and Treatment

BACKGROUND

Keloid and hypertrophic scars represent an aberrant response to the wound healing process. These scars are characterized by dysregulated growth with excessive collagen formation, and can be cosmetically and functionally disruptive to patients.

OBJECTIVE

Objectives are to describe the pathophysiology of keloid and hypertrophic scar, and to compare differences with the normal wound healing process. The classification of keloids and hypertrophic scars are then discussed. Finally, various treatment options including prevention, conventional therapies, surgical therapies, and adjuvant therapies are described in detail.

MATERIALS AND METHODS

Literature review was performed identifying relevant publications pertaining to the pathophysiology, classification, and treatment of keloid and hypertrophic scars.

RESULTS

Though the pathophysiology of keloid and hypertrophic scars is not completely known, various cytokines have been implicated, including interleukin (IL)-6, IL-8, and IL-10, as well as various growth factors including transforming growth factor-beta and platelet-derived growth factor. Numerous treatments have been studied for keloid and hypertrophic scars,which include conventional therapies such as occlusive dressings, compression therapy, and steroids; surgical therapies such as excision and cryosurgery; and adjuvant and emerging therapies including radiation therapy, interferon, 5-fluorouracil, imiquimod, tacrolimus, sirolimus, bleomycin, doxorubicin, transforming growth factor-beta, epidermal growth factor, verapamil, retinoic acid, tamoxifen, botulinum toxin A, onion extract, silicone-based camouflage, hydrogel scaffold, and skin tension offloading device.

CONCLUSION

Keloid and hypertrophic scars remain a challenging condition, with potential cosmetic and functional consequences to patients. Several therapies exist which function through different mechanisms. Better understanding into the pathogenesis will allow for development of newer and more targeted therapies in the future.

The role of histamine in the regulation of the viability, proliferation and transforming growth factor β1 secretion of rat wound fibroblasts

BACKGROUND

Inflammation mediators play a regulatory role in repair processes. The study will examine the influence of histamine on wound fibroblast metabolic activity, viability, proliferation, and TGFβ1 secretion. The study also will identify the histamine receptor involved in regulation of the tested repair processes.

METHODS

Fibroblasts were obtained from the granulation tissue of wounds or intact dermis of rats. The MTT and BrdU assays were used to examine the effect of histamine (10^-8M-10^-4M) on the viability and metabolic activity of fibroblasts, and on their proliferative capacity. The influence of histamine receptor antagonists (i.e., ketotifen, ranitidine, ciproxifan and JNJ7777120) and agonists (2-pyridylethlamine dihydrochloride, amthamine dihydrobromide) was also investigated. The TGFβ1 and histamine receptors H1 were evaluated by enzyme-linked immunosorbent assay.

RESULTS

Histamine significantly increased granulation tissue fibroblast viability and metabolic activity at 10^-8 and 10^-6M but did not change their proliferative activity. Only the blockade of the H1 receptor removed this effect of histamine. H1 receptor agonist (2-pyridylethlamine dihydrochloride) increased cell viability, thereby mimicking histamine action. Both Histamine (10^-4M) and 2-pyridylethlamine dihydrochloride increased TGFβ1 concentration in cell culture medium. However, ketotifen blocked histamine-induced augmentation of TGFβ1. H1 receptor expression on wound fibroblasts was confirmed.

CONCLUSION

The regulatory influence of histamine on wound fibroblast function (viability/metabolic activity or secretion of TGFβ1) is dependent on H1 receptor stimulation. Contrary to wound fibroblasts, these cells express a very low level of H1 receptors when isolated from intact dermis and histamine is unable to modify their metabolic activity.

Controlling Arteriogenesis and Mast Cells Are Central to Bioengineering Solutions for Critical Bone Defect Repair Using Allografts

Although most fractures heal, critical defects in bone fail due to aberrant differentiation of mesenchymal stem cells towards fibrosis rather than osteogenesis. While conventional bioengineering solutions to this problem have focused on enhancing angiogenesis, which is required for bone formation, recent studies have shown that fibrotic non-unions are associated with arteriogenesis in the center of the defect and accumulation of mast cells around large blood vessels. Recently, recombinant parathyroid hormone (rPTH; teriparatide; Forteo) therapy have shown to have anti-fibrotic effects on non-unions and critical bone defects due to inhibition of arteriogenesis and mast cell numbers within the healing bone. As this new direction holds great promise towards a solution for significant clinical hurdles in craniofacial reconstruction and limb salvage procedures, this work reviews the current state of the field, and provides insights as to how teriparatide therapy could be used as an adjuvant for healing critical defects in bone. Finally, as teriparatide therapy is contraindicated in the setting of cancer, which constitutes a large subset of these patients, we describe early findings of adjuvant therapies that may present future promise by directly inhibiting arteriogenesis and mast cell accumulation at the defect site.

The molecular basis of hypertrophic scars

Hypertrophic scars (HTS) are caused by dermal injuries such as trauma and burns to the deep dermis, which are red, raised, itchy and painful. They can cause cosmetic disfigurement or contractures if craniofacial areas or mobile region of the skin are affected. Abnormal wound healing with more extracellular matrix deposition than degradation will result in HTS formation. This review will introduce the physiology of wound healing, dermal HTS formation, treatment and difference with keloids in the skin, and it also review the current advance of molecular basis of HTS including the involvement of cytokines, growth factors, and macrophages via chemokine pathway, to bring insights for future prevention and treatment of HTS.

Stimulatory effects of histamine on migration of nasal fibroblasts

BACKGROUND

Fibroblast migration is crucial for normal wound repair after sinonasal surgery. Histamine is known to be involved in wound healing by its effects on cell proliferation and migration. This study aimed to determine whether histamine affects the migration of nasal fibroblasts and to investigate the mechanism of action of histamine on nasal fibroblasts.

METHODS

Primary cultures of nasal fibroblasts were established from inferior turbinate samples. Fibroblast migration was evaluated with scratch assays. Cells were treated with histamine and/or histamine receptor-selective antagonists. U-73122 and pertussis toxin, which are selective inhibitors of the lower signaling pathway of H1R and H4R, were used to confirm the modulation of nasal fibroblast migration by histamine. Fibroblast cytoskeletal structures were visualized with immunocytochemistry.

RESULTS

Histamine significantly stimulated the migration of nasal fibroblasts. Antagonists selective for HR1 and HR4 significantly reduced nasal fibroblast migration. In immunocytochemical staining, histamine treatment increased membrane ruffling and pyrilamine, diphenhydramine, fexofenadine, and JNJ7777120 decreased histamine-induced membrane ruffling. U-73122 and pertussis toxin also decreased histamine-induced migration of fibroblasts. Histamine maintains its stimulatory effects on fibroblast migration in the presence of mitomycin C, which blocks proliferation of cells.

CONCLUSION

We showed that histamine stimulates fibroblast migration in nasal fibroblasts. This effect appeared to be mediated by HR1 and HR4. However, because fibroblast migration also can be involved in scaring and fibrosis, more research is necessary to determine the effects of antihistamine on wound healing after sinus surgery.

The Importance of Mast Cells in Dermal Scarring

Significance: Mast cells are resident inflammatory cells present in high numbers in the skin. They are one of the first cell types to respond to damage and they do so by quickly releasing a variety of preformed mediators that are stored within mast cell granules. Mast cells are not only active early on, where they help induce inflammation, but they also stimulate the proliferation of several important cell types and influence the production and remodeling of collagen. Recent Advances: Recent studies have highlighted the importance of mast cells in determining the amount of scar tissue that forms as a result of the repair process. Mast cells are found in low numbers and in a less activated state in scarless wounds, whereas high numbers of activated mast cells are associated with scarring and fibrosis. Furthermore, animals that lack mast cells or have been treated with degranulation inhibitors or drugs that block the activity of mast cell proteases have been shown to heal with reduced scar tissue. Critical Issues: Despite evidence suggesting that mast cells regulate scar tissue development, the entire range of mast cell activities during wound repair and scar formation has not been completely characterized. In addition, the potential therapeutic benefits of targeting mast cells clinically have yet to be fully explored. Future Directions: More studies are needed to determine whether inhibiting mast cell activation and blocking the function of mast cell mediators are viable options to prevent or reduce the appearance of scars.

Development of mast cells and importance of their tryptase and chymase serine proteases in inflammation and wound healing

Mast cells (MCs) are active participants in blood coagulation and innate and acquired immunity. This review focuses on the development of mouse and human MCs, as well as the involvement of their granule serine proteases in inflammation and the connective tissue remodeling that occurs during the different phases of the healing process of wounded skin and other organs. The accumulated data suggest that MCs, their tryptases, and their chymases play important roles in tissue repair. While MCs initially promote healing, they can be detrimental if they are chronically stimulated or if too many MCs become activated at the same time. The possibility that MCs and their granule serine proteases contribute to the formation of keloid and hypertrophic scars makes them potential targets for therapeutic intervention in the repair of damaged skin.

Mast cell activity in the healing wound: more than meets the eye?

Mast cells (MCs) are an important part of the innate immune system and are abundant in barrier organs such as the skin. They are known primarily for initiating allergic reactions, but many other biological functions have now been described for these cells. Studies have indicated that during wound repair, MCs enhance acute inflammation, stimulate reepithelialization and angiogenesis, and promote scarring. MCs have also been linked to abnormal healing, with high numbers of MCs observed in chronic wounds, hypertrophic scars and keloids. Although MCs have gained attention in the wound healing field, several unique features of MCs have yet to be examined in the context of cutaneous repair. These include the ability of MCs to: (i) produce anti-inflammatory mediators; (ii) release mediators without degranulating; and (iii) change their phenotype. Recent findings highlight the complexity of MCs and suggest that more information is needed to understand their complete range of activities during repair.

Examining the role of mast cells in fetal wound healing using cultured cells in vitro

Mast cells play an important role during the inflammatory phase of wound healing, and studies suggest that they also influence scar formation and remodeling. Recently, our laboratory has characterized the mast cell response to injury in a fetal wound healing model. In this model, early gestation fetal skin regenerates and heals without a scar (scarless wounds) and late gestation skin heals with a scar (fibrotic wounds). Differences in mast cell number, maturity, and activity were identified between scarless and scar-forming fetal wounds. To study mast cell function in more detail, in vitro experiments are useful. This chapter outlines methods to expand, purify, and study the function of mast cells harvested from murine fetal skin. Using these methods, cultured mast cells retain many of the differences in maturity and activation seen during fetal skin development in vivo. Studying the function of mast cells in vitro could help define the mechanisms by which mast cells contribute to wound repair and ultimately lead to better therapies for improving wound repair and reducing scar formation.

Pain mediators and wound healing--establishing the connection

Pain accompanies every disruption of the skin surface in a normal sensate individual. The intensity and duration of the pain varies depending on the nature of trauma, the healing trajectory and various host factors. Pain mediator release is the mechanism for pain perception following peripheral stimulus and central interpretation. The various mediators may have promoting effects on wound healing in the short term, but it appears that protracted release of these mediators may well have detrimental effects on wound healing. The exaggerated release of pain mediators may result in nociceptor hypersensitization, hyperinflammatory cellular and extracellular matrix (ECM) changes, and in some cases, the potential for a fibrotic healing pattern. This relates to an imbalance between mediators with differing healing characteristics arising in certain pathological conditions. In this respect, it may be worth examining pain mediator agonists or antagonists, not only on compassionate grounds of pain control, but relating to the potential effects on overall wound healing.

Histidine decarboxylase expression influences the neofolliculogenesis of newborn mouse dermal cells

BACKGROUND

With the introduction of hair regeneration techniques using epidermal and dermal cells, hair follicle regeneration became much easier and faster. Current success has been dependent on the availability of cells from newborn or embryonic mice. We recently observed that the hair-inducing ability of newborn mouse dermal cells disappeared in the first few days of life and there was a drastic decrease of histidine decarboxylase (HDC) gene expression from postnatal day 0 (p0) to day 7 (p7).

OBJECTIVE

The aim of this study was to study the role of HDC in hair follicle induction.

METHODS

The mRNA levels of HDC in p0, p7 and p48 C57BL/6 mouse skin were checked with a real time reverse transcription polymerase chain reaction and immunohistochemistry. To test the effect of HDC, HDC expression in p0 mouse dermal cells was suppressed with small interfering RNA (siRNA) transfection. Mock treated and HDC siRNA treated cells were then injected with adult epidermal cells into nude mice skin. Three weeks later, the number, length and thickness of induced hairs were compared.

RESULTS

Compared with p0, the mRNA level of HDC was much lower at p7 and p48. Immunohistochemical staining also revealed a marked decrease of HDC expression in p7 mice skin, compared with p0 skin. Hair patch assays showed that the HDC siRNA treated p0 dermal cells induced less hair follicle structures and shorter and thinner hair shafts than mock treated cells.

CONCLUSION

HDC, whose expression is remarkably downregulated during the first few days after birth in dermal cells of mice, plays essential roles in the hair-inducing ability of newborn mouse dermal cells.

Mast cells contribute to scar formation during fetal wound healing

Scar formation is a potentially detrimental process of tissue restoration in adults, affecting organ form and function. During fetal development, cutaneous wounds heal without inflammation or scarring at early stages of development, but begin to heal with significant inflammation and scarring as the skin becomes more mature. One possible cell type that could regulate the change from scarless to fibrotic healing is the mast cell. We show here that dermal mast cells in scarless wounds generated at embryonic day 15 (E15) are fewer in number, less mature and do not degranulate in response to wounding as effectively as mast cells of fibrotic wounds made at embryonic day 18 (E18). Differences were also observed between cultured mast cells from E15 and E18 skin with regard to degranulation and preformed cytokine levels. Injection of mast cell lysates into E15 wounds disrupted scarless healing, suggesting that mast cells interfere with scarless repair. Finally, wounds produced at E18, which normally heal with a scar, healed with significantly smaller scars in mast cell-deficient Kit^W/W-v mice compared to Kit^+/+ littermates. Together, these data suggest that mast cells enhance scar formation, and that these cells may mediate the transition from scarless to fibrotic healing during fetal development.

Modulatory effects of connexin-43 expression on gap junction intercellular communications with mast cells and fibroblasts

The influence of mast cells upon aberrant wound repair and excessive fibrosis has supportive evidence, but the mechanism for these mast cell activities is unclear. It is proposed that heterocellular gap junction intercellular communication (GJIC) between fibroblasts and mast cells directs some fibroblast activities. An in vitro model was used employing a rodent derived peritoneal mast cell line (RMC-1) and human dermal derived fibroblasts. The influence of the expression of the gap junction channel structural protein, connexin 43 (Cx-43) on heterocellular GJIC, the expression of microtubule β-tubulin and microfilament α smooth muscle actin (SMA) were investigated. The knockdown of Cx-43 by siRNA in RMC-1 cells completely blocked GJIC between RMC-1 cells. SiRNA knockdown of Cx-43 within fibroblasts only dampened GJIC between fibroblasts. It appears Cx-43 is the only expressed connexin (Cx) in RMC-1 cells. Fibroblasts express other Cxs that participate in GJIC between fibroblasts in the absence of Cx-43 expression. Heterocellular GJIC between RMC-1 cells and fibroblasts transformed fibroblasts into myofibroblasts, expressing α SMA within cytoplasmic stress fibers. The knockdown of Cx-43 in RMC-1 cells increased β-tubulin expression, but its knockdown in fibroblasts reduced β-tubulin expression. Knocking down the expression of Cx-43 in fibroblasts limited αSMA expression. Cx-43 participation is critical for heterocellular GJIC between mast cells and fibroblasts, which may herald a novel direction for controlling fibrosis.

Cellular/extracellular matrix cross-talk in scar evolution and control

The principles of scar evolution and control are recognized and defined. Further clarity has been shed on these principles with the elucidation and elaboration of the sequence of events occurring at a molecular level. Cellular cross-talk among structures in the cell cytosol, in the cellular nucleus, and outside the cell within in the extracellular matrix is continuous and controlling in nature. This interaction or "dynamic reciprocity" takes place via a series of signals, ionic messenger shifts, protein activation, and receptor transactions. The described principles are now able to be defined in terms of cellular/extracellular matrix interactions and the identification of the cross-talk involved in scar evolution and maturation presents the possibility of influencing the "wording" of this cross-talk to improve scar outcome. The principles of mechanostimulation and scar support, hydration occlusion, controlled inflammation, and collagen/extracellular remodeling are discussed with possible interventions in each category.

Hypertrophic scar in a dog: histological and clinical features

An adult male bullmastiff dog was treated for paraparesis and ataxia due to discospondylitis and disc herniation. At this time, the dog had a nonhealing ulcer between the pads of the left hindfoot. At re-evaluation, the dog had developed a large exophitic mass in the previously ulcerated area. Cytological examination revealed occasional spindle cells with mild atypia, and a soft tissue tumour was suspected. The mass was excised and submitted for histology. The lesion was characterized by superficial ulceration, an intermediate layer of granulation tissue and a deep portion containing vertically orientated capillaries and perpendicularly arranged fibroblasts and collagen. The histological features led to a diagnosis of hypertrophic scar. Eight weeks after surgery, the lesion recurred and was treated with an intralesional injection of methylprednisolone acetate. The lesion regressed in 10 days, but recurred after 3 months following severe self-trauma. Hypertrophic scars and keloids are two types of exuberant scarring reported in human beings, the pathogenesis of which is still unclear but seems to involve several cytokines, growth factors and inflammatory cells. The histological features identified in this case paralleled those reported in hypertrophic scars in humans. In this case, intralesional corticosteroid therapy was useful in the management of the lesion, but the severe self-trauma could have influenced the recurrence. Even if uncommon, hypertrophic scar should be included among the differential diagnoses of spindle cell tumours in dogs.

Peritoneal cell response during adhesion formation

BACKGROUND

We estimated a number of cell populations of peritoneal fluid in rats with experimentally developed peritoneal adhesions.

MATERIALS AND METHODS

The fluid was taken in standarized conditions at the first operation and during reoperation. Animals were divided into four groups. The first group was the control group (n = 20) on which the abdomen was opened and closed without any manipulations (group 1a), and the reoperation was done after 72 hr (group 1b). The other groups (2, 3, 4; n = 20 for each group) were operated, and scarification of the parietal peritoneum and serosa of the bowel was performed. The rats were reoperated after 24, 72, and 168 hr, respectively, after the first surgery. The peritoneal cavity was washed with the 0.9% saline solution. The number of the peritoneal adhesions and populations of the cells were counted.

RESULTS

The highest number of peritoneal adhesions was observed in the group of animals reoperated after 72 hr. After 72 and 168 hr, the higher number of mast cells (MC) and neutrophils was observed. The difference was statistically significant. The percentage of mast cells (MC) increased during the experiment. It was different from other cell populations which decreased after 168 hr. The highest change in number was observed for MC. The highest number of MC was observed on the seventh day after the laparotomy.

CONCLUSIONS

MC influence peritoneal adhesion formation and probably take part in adhesion remodeling. MC and neutrophils changed significantly after manipulations in the peritoneal cavity. Probably, they play an important role in peritoneal adhesion formation.

Mast cells in peritoneal fluid in rats with experimentally induced peritoneal adhesions

Mast cells (MC) produce, store and release many biologically active substances, especially inflammatory factors, chemotactic substances for neutrophiles, cytokines and prostaglandins. They play very important role in fibrinosis and they are an important factor in peritoneal adhesions formation and lysis. In this study we tried to evaluate role of mast cells in peritoneal adhesions formation. We estimated number of mast cells in peritoneal fluid in rats with experimentally developed peritoneal adhesions. The number of mast cells per ml was counted in flow cytometry in specimens of peritoneal fluid taken from operated rats. The fluid was taken in standardized conditions the same for each group at the first operation and during reoperation. Peritoneal cavity was washed with 0.9% Saline solution. MC were visualized using indirect immunohistochemical method LSAB with mouse antibody. The animals were divided into 4 groups. 1 st group was control group (n=20) on which the abdomen was opened and closed without any manipulations, and the reoperation was done after 72 hours. The other groups (2, 3, 4; n=20 for each group) were operated and scarification of the partial peritoneum and serosa was performed. The rats were brought back to conscious and then were reoperated respectively after 24, 72 and 168 hours after first surgery. After the laparotomy and damage of the peritoneum we observed formation of the peritoneal adhesions between intestine loops and between intestines and damaged parietal peritoneum. Also the higher number of mast cells was observed in the groups of animals with damaged peritoneum. The highest number of peritoneal adhesions was observed in the group of animals reoperated after 72 hours. After 72 and 168 hours the higher number of MC and neutrophils was observed. The difference was statistically significant. The percentage of mast cells was increasing during the experiment duration. It was different from other cells populations which decreased after 168 hours. The MC and neutrophils were cell population which changed significantly after manipulations in peritoneal cavity. It is very probable that they play an important role in peritoneal adhesions formation.

MAST CELLS INDUCE ACTIVATION OF HUMAN LUNG FIBROBLASTS IN VITRO

Mast cells are able to induce proliferation of skin fibroblasts; however, their effect on lung fibroblasts has not been clearly established. Using in vitro cocultures of rat or human mast cells with lung fibroblasts, the authors determined whether mast cells alter proliferation, collagen synthesis, and metalloproteinase production from lung fibroblasts. Mast cells enhanced the proliferation of human fibroblasts (mean +/- SEM: 90% +/- 4.7% increase, P < .001) while inhibiting fibroblast collagen synthesis (48.1% +/- 4.2% decrease, P < .001). Histamine, but not tryptase, significantly enhanced fibroblast proliferation: 92% +/- 5.8% (P < .001) and 39.2% +/- 4.3% (P > 0.05), respectively. Rat mast cell sonicate added to lung fibroblasts induced the activation of metalloproteinase-9 while inhibiting that of metaloproteinase-2. The addition of lipopolysaccharide (LPS)-stimulated lung macrophage supernatant further enhanced the poliferative effect of mast cells on fibroblasts (by 60% +/- 7.8%, P < .001) and induced synthesis of collagen from these cells (190% +/- 28% increase versus control, P < .05). This study demonstrates that mast cells influence several aspects of lung fibroblast function in vitro.

Potential cellular and molecular causes of hypertrophic scar formation

A scar is an expected result of wound healing. However, in some individuals, and particularly in burn victims, the wound healing processes may lead to a fibrotic hypertrophic scar, which is raised, red, inflexible and responsible for serious functional and cosmetic problems. It seems that a wide array of subsequent processes are involved in hypertrophic scar formation, like an affected haemostasis, exaggerated inflammation, prolonged reepithelialization, overabundant extracellular matrix production, augmented neovascularization, atypical extracellular matrix remodeling and reduced apoptosis. Platelets, macrophages, T-lymphocytes, mast cells, Langerhans cells and keratinocytes are directly and indirectly involved in the activation of fibroblasts, which in turn produce excess extracellular matrix. Following the chronology of normal wound healing, we unravel, clarify and reorganize the complex molecular and cellular key processes that may be responsible for hypertrophic scars. It remains unclear whether these processes are a cause or a consequence of unusual scar tissue formation, but raising evidence exists that immunological responses early following wounding play an important role. Therefore, when developing preventive treatment modalities, one should aim to put the early affected wound healing processes back on track as quickly as possible.

The accelerating effect of histamine on the cutaneous wound-healing process through the action of basic fibroblast growth factor

This study revealed that the absence of histamine in histidine decarboxylase gene-knockout (HDC(-/-)) mice resulted in delayed cutaneous wound healing and that exogenously administered histamine compensated this process. With the overproduction of histamine in HDC gene-transgenic mice, the healing was accelerated compared to the HDC(+/+) mice. These results indicate that histamine positively accelerated the cutaneous wound healing. Macrophage recruitment and angiogenesis at the wound edge were specifically impaired in HDC(-/-) mice, and histamine-treated wounds in HDC(-/-) mice demonstrated increased macrophage recruitment and angiogenesis. The amount of basic fibroblast growth factor (bFGF) in protein level at the wound edge was higher in HDC(+/+) mice, especially on the 3rd and 5th day of wound healing compared to those in HDC(-/-) mice. Topically administered SU5402, a specific antagonist to fibroblast growth factor receptor-1 tyrosine kinase, to the wound surface suppressed the wound healing in HDC(+/+) mice but not in HDC(-/-) mice. Moreover, SU5402 reduced macrophage recruitment and angiogenesis in HDC(+/+) mice. From these observations, it was concluded that the accelerated wound-healing activity of histamine was mediated by the activity of bFGF, which leads to angiogenesis, and macrophage recruitment in the wound-healing process.

CD117-positive cells and mast cells in adult human cardiac valves—observations and implications for the creation of bioengineered grafts

BACKGROUND

There is no report to date of stem cells in human cardiac valves. We examined their possible presence, number, and distribution in valves removed at cardiac surgery from patients with a variety of underlying valve pathologies.

METHODS

Grossly normal aortic and mitral valves were obtained from live heart transplant patients. Surgically excised valves with rheumatic mitral stenosis, aortic valve age-related degeneration, aortic valve changes of aortoannular ectasia, and mitral valves with myxomatous degeneration were studied. Immunohistochemical and histochemical studies were performed on sequential valve sections, including hematoxylin and eosin, hematoxylin phloxine saffron, Movat pentachrome, toluidine blue, CD31, CD34, and CD117.

RESULTS

There were small clusters of CD117-positive cells in the fibrosa and spongiosa of mitral and aortic valves from all groups of valves. Sequential sectioning and staining showed that almost all of these cells were mast cells. However, in the mitral myxomatous valves and the mitral rheumatic valves, there were rare CD117-positive cells that did not have corresponding toluidine blue staining and thus could be valve mesenchymal stem cells.

CONCLUSIONS

Most of the CD117-positive cells in normal and diseased adult heart valves are mast cells. These valve cells could play a role in valve pathology and injury. A very small number of possible valve stem cells were also identified. It is unlikely that these valve stem cells are sufficient in number to allow isolation and expansion for tissue engineering purposes.

Substance P Levels and Neutral Endopeptidase Activity in Acute Burn Wounds and Hypertrophic Scar

BACKGROUND

Substance P, a cutaneous neuroinflammatory mediator released from peripheral nerves, plays a role in responses to injury. Neutral endopeptidase is a cell membrane-bound metallopeptidase enzyme that regulates substance P activity. The question of substance P involvement in hypertrophic scar development has been based on observations that hypertrophic scars have increased numbers of nerves. The authors hypothesized that hypertrophic scar has greater substance P levels and decreased neutral endopeptidase activity compared with uninjured skin and acute partial-thickness burns, which may contribute to an exuberant response to injury.

METHODS

The authors obtained small skin samples of deep partial-thickness burns (n = 7; postburn days 7 to 78) and uninjured skin (n = 14) from patients (eight male patients and six female patients; 2 to 71 years old) undergoing burn wound excision. Hypertrophic scar samples were obtained from six patients (three male patients and three female patients; 8 to 47 years old) undergoing surgical excision 13 to 64 months after burn injury. Protein concentrations were determined using a bicinchoninic acid assay. Substance P concentration was determined by means of indirect enzyme-linked immunosorbent assay. Neutral endopeptidase activity was measured using an enzymatic assay that quantifies a fluorescent degradation product, methoxy-2-naphthylamine (MNA). Substance P and neutral endopeptidase data were standardized to sample weight.

RESULTS

Substance P levels were greater in hypertrophic scar (3506 pg/g) compared with uninjured skin (1698 pg/g; p < 0.03) and burned skin (958 pg/g; p < 0.01). Hypertrophic scar samples had decreased neutral endopeptidase enzyme activity (8.8 pM MNA/hour/microg) compared with normal skin (16.3 pM MNA/hour/microg; p < 0.05). Acute burn wounds (27.9 pM MNA/hour/microg) demonstrated increased neutral endopeptidase enzyme activity (p < 0.05).

CONCLUSIONS

Increased substance P concentration in hypertrophic scar correlates with histologic findings of increased nerve numbers in hypertrophic scar samples. Decreased neutral endopeptidase enzyme activity in hypertrophic scar may contribute to increased available substance P that may result in an exuberant neuroinflammatory response.

Regulation of activin A expression in mast cells and asthma: its effect on the proliferation of human airway smooth muscle cells

Activin A, a homodimeric protein (betaAbetaA) and a member of the TGF-beta superfamily, is involved in the inflammatory repair process. Using cDNA microarray analysis, we discovered strong induction of the activin betaA gene in human mast cells (MC) on stimulation with PMA and calcium ionophore (A23187). Activin betaA mRNA was also highly induced in primary cultured murine bone marrow MC (BMMC) after stimulation by IgE receptor cross-linking. Secretion of activin A was evident in human mast cell-1 line cells 3 h after stimulation and progressively increased over time. Activin A was present in the cytoplasm of activated but not unstimulated murine bone marrow MC as demonstrated by immunofluorescence studies, suggesting that secretion of activin A by MC was due to de novo synthesis rather than secretion of preformed protein. Activin A also colocalized with human lung MC from patients with asthma by double-immunofluorescence staining. Furthermore, secretion of activin A was significantly increased in the airway of wild-type mice after OVA sensitization followed by intranasal challenge. Secretion of activin A, however, was greatly reduced in MC-deficient WBB6F(1)-W/W(v) mice as compared with wild-type mice, indicating that MC are an important contributor of activin A in the airways of a murine asthma model. Additionally, activin A promoted the proliferation of human airway smooth muscle cells. Taken together, these data suggest that MC-derived activin A may play an important role in the process of airway remodeling by promoting the proliferation of airway smooth muscle.

Mast cells in tissue response to dentistry materials: an adhesive resin, a calcium hydroxide and a glass ionomer cement

Synthetic materials used in dentistry may trigger various inflammatory responses. In order to evaluate biocompatibility, standardized implants of Calcium Hydroxide (CH), Glass Ionomer Cement (GIC) and Light-activated Dental Adhesive (LDA) were surgically introduced into Wistar rats' back bone. Six (experimental) animal groups, five each, and two Sham (S) groups were studied after 15 and 30 days from surgery. In each animal, the density of mast cells and interstitial fibrosis volume was evaluated by quantitative light microscopy. In addition, the interaction between the disk material and its fibrous capsule was evaluated by scanning electron microscopy. The density of mast cells per area (N(A)[mast cells]) was lower in CH group than in LDA group. GIC group displayed N(A)[mast cells] results intermediate between CH and LDA groups (p<0.05). The smallest interstitial fibrosis volume density (Vv[f]) was observed in CH group, then in GIC group, while the greatest in LDA group. After 30 days, the fibrosis in LDA group was 30% higher than in CH group (p<0.05). In S group, discreet fibrosis restricted to surgical area was present, with few mast cells near the vessels. Significant interaction between fibrous capsule and the surrounding disk material was most evident in CH group. The implanted materials induced mast cell migration, distinct fibrosis development, suggesting that CH is the most biocompatible material among those tested.

Development of the single-cell MALDI-TOF (matrix-assisted laser desorption/ionization time-of-flight) mass-spectroscopic assay

MALDI-TOF mass spectrometry was used to detect intracellular molecules from a single intact cell on monolayers of other cells. Intracellular molecules, e.g., histamine, were gradually increased in a mouse bone marrow-derived mast cell by a maturation process. A single cell was captured by a microsuction pipette, and the mass spectra of intracellular histamine were measured directly. Finally, the time course of the intracellular molecular contents and the maturation stage from a single cell were estimated.

Role of mast cells and myofibroblasts in human peritoneal adhesion formation

OBJECTIVE

To study fibroblasts and mast cells in human peritoneal adhesions and to evaluate whether their interaction plays a role in adhesion development.

SUMMARY BACKGROUND DATA

Myofibroblasts play a critical role in wound repair/fibrosis. Mast cells influence the formation of peritoneal adhesions in a rat model, and they are modulators of fibroblast functions.

METHODS

Peritoneal adhesion biopsies were processed for either histology (H&E, toluidine blue) or immunohistochemistry (tryptase, laminin, collagen type IV and VIII, and alpha-SMA) or grown as explants for obtention of fibroblasts. The effects of mast cell (HMC-1) sonicate and selected mast cell mediators and cytokines on fibroblast proliferation ([ (3)H]thymidine) and collagen synthesis ([ (3)H]proline) and on fibroblast contractile activity (tridimensional collagen lattice) were evaluated. Mast cell mediators influencing fibroblast proliferation were partially characterized by enzymatic susceptibility and FPLC gel filtration column chromatography.

RESULTS

Most of the fibroblasts in peritoneal adhesions were identified as alpha-SMA-positive myofibroblasts. Mast cell hyperplasia was observed and more than one third of the mast cells were degranulated. Few mast cells showed a faint staining for laminin or collagen type IV and VIII. Mast cell sonicate increased fibroblast proliferation and contractile activity while decreasing collagen synthesis. Mast cell sonicate proliferating activities were found to be proteinase-sensitive with a molecular weight of more than 158 kd, of approximately 40 kd, and of less than 10 kd. TGF-beta and tryptase enhanced collagen synthesis; TNF-alpha and chymase decreased it. None of the selected mediators increased fibroblast proliferation.

CONCLUSIONS

Myofibroblasts are the main connective tissue cells present in human peritoneal adhesions, and mast cells play a direct role in peritoneal adhesion formation.

Effect of Mederma on hypertrophic scarring in the rabbit ear model

Currently accepted conservative treatments of hypertrophic scars are limited to steroid injections, radiation therapy, and silicone occlusive therapy. However, the use of Mederma for these problematic lesions has become quite prevalent in the clinical setting. Little scientific evidence exists to support the efficacy of this product in reducing hypertrophic scars. The aim of this study was to study the effects of Mederma on hypertrophic scars in the rabbit hypertrophic scar model, allowing the histologic quantification of scar elevation, dermal collagen organization, vascularity, and inflammation and the gross examination of scar erythema. Full-thickness wounds down to cartilage, four per ear, were created in four New Zealand White rabbits, for a total of 32 scars. Twenty-eight days after the initial wounding, the hypertrophic scars were photographed, and treatment of half of the scars on each ear was begun with Mederma three times per day for a total of 4 weeks. The untreated scars served as control scars and were left exposed to air. After 4 weeks of treatment, the scars were once again photographed. The rabbits were then killed, and the scars were analyzed histologically. The pretreatment and posttreatment photographs were compared by using computer quantification of magenta, yellow, and cyan expression within the scars. Histologic analysis demonstrated no significant reduction in scar hypertrophy or scar elevation index. However, a significant improvement in dermal collagen organization was noted on comparing Mederma-treated scars with untreated control scars (p < 0.05). No significant difference in dermal vascularity or inflammation was noted. Computer analysis of the scar photographs demonstrated no significant reduction in scar erythema with Mederma treatment. The active product in Mederma, allium cepa, has as its derivative quercetin, a bioflavonoid noted for its antiproliferative effects on both normal and malignant cells, and its antihistamine release effects. These properties could theoretically prove beneficial in reversing the inflammatory and proliferative responses noted in hypertrophic scars. Despite the authors' inability to demonstrate a reduction in scar hypertrophy, the improvement in collagen organization noted in the Mederma-treated scars suggests it may have an effect on the pathophysiology of hypertrophic scar formation.

Mast cell-fibroblast interactions: human mast cells as source and inducers of fibroblast and epithelial growth factors

As mast cells have been implicated in cutaneous repair processes, we have examined the ability of human mast cells to produce important epithelial and fibroblast growth factors or to stimulate the production of such factors in dermal fibroblasts. Isolated, highly purified human dermal mast cells and human leukemic mast cells were examined for mRNA and partly also for protein expression of these molecules as such or after preincubation with interleukin-4, stem cell factor, or with phorbol myristate acetate. In addition, mast cells were studied for their ability to induce fibroblast growth factor 2 and fibroblast growth factor 7 secretion from dermal fibroblasts. Both dermal and leukemic mast cells expressed fibroblast growth factor 2, fibroblast growth factor 7, and heparin-binding epidermal growth factor, but not hepatocyte growth factor at mRNA level, and dermal mast cells expressed fibroblast growth factor 10 in addition. At protein level, spontaneous fibroblast growth factor 2 secretion was noted that was markedly enhanced by phorbol myristate acetate, whereas no fibroblast growth factor 7 protein was detected under these conditions. Instead, human mast cell-1 supernatants induced enhanced fibroblast growth factor 7 secretion from dermal fibroblasts, with phorbol-myristate-acetate-stimulated supernatants being more effective. This effect could be reproduced with histamine and was H1-receptor mediated. Tryptase was ineffective but stimulated instead fibroblast growth factor 2 secretion from fibroblasts. These data demonstrate for the first time the ability of mast cells to express and/or secrete several growth factors of the fibroblast growth factor family as well as heparin-binding epidermal growth factor directly or indirectly via stimulation of fibroblasts, underlining the potentially pivotal role of these cells during human tissue repair and homeostasis.

Human mast cells stimulate fibroblast proliferation, collagen synthesis and lattice contraction: a direct role for mast cells in skin fibrosis

BACKGROUND

Mast cells, the key cells of immediate hypersensitivity type reactions, have also been postulated to have a central role in influencing tissue remodelling and fibrosis occurring in the skin.

OBJECTIVE

Our aim was to investigate the direct role of human mast cells (HMC) in skin fibrotic processes, by assessing the effects of the addition of the human mast cell line HMC-1 to human skin fibroblasts, and to identify the responsible mediators.

METHODS

HMC-1 sonicates were added to human skin fibroblasts and the following parameters were evaluated: proliferation ([3H]-thymidine), collagen synthesis ([3H] proline), activity of matrix metalloproteinases (MMPs) (zymography) and tissue inhibitors of metalloproteinases (TIMPs) (reverse zymography), and collagen gel contraction.

RESULTS

HMC-1 sonicate increased significantly both proliferation and collagen production in the human skin fibroblasts and these properties were not affected by heating of the sonicate (56 degrees C, 30 min, or 100 degrees C, 3 min). Two main mast cell mediators, histamine and tryptase, were found to be responsible for the increase in fibroblast proliferation and collagen production. HMC-1 sonicate did not display any pre-formed gelatinase activity, and its addition to the fibroblasts did not change their pro-MMP-2 and MMP-2 activity. On the other hand, HMC-1 were found to possess TIMP-1 and TIMP-2. Addition of HMC-1 had no effect on fibroblasts TIMP-1 but induced a dose-dependent increase of TIMP-2 activity. In addition, HMC-1 sonicate seeded together with the fibroblasts in tri-dimensional collagen gel significantly enhanced their contraction.

CONCLUSION

We have shown that human mast cells, by granule-stored and therefore quickly releasable mediators, increase human skin fibroblast proliferation, collagen synthesis, TIMP-2 and collagen gel contraction. Therefore, mast cells have a direct and potentiating role in skin remodelling and fibrosis.

The mast cell in wound healing

This review describes the role of the mast cell in the pathobiology of skin healing. After illustrating its main morphofunctional characteristics, with special reference to the dog and cat, we consider the involvement of the mast cell in the various phases of skin repair. With the aid of a wide array of newly formed or preformed mediators released by degranulation, the activated mast cell controls the key events of the healing phases: triggering and modulation of the inflammatory stage, proliferation of connective cellular elements and final remodelling of the newly formed connective tissue matrix. The importance of the mast cell in regulating healing processes is also demonstrated by the fact that a surplus or deficit of degranulated biological mediators causes impaired repair, with the formation of exuberant granulation tissue (e.g. keloids and hypertrophic scars), delayed closure (dehiscence) and chronicity of the inflammatory stage.

The differentiation and function of myofibroblasts is regulated by mast cell mediators

Myofibroblasts are fibroblasts that express certain features of smooth muscle differentiation. Increased numbers of myofibroblasts and mast cells are frequently found together in a wide variety of settings, such as normal wound repair and scleroderma skin, which suggests that mediators produced by the mast cells could play a role in the regulation of myofibroblast differentiation and function. We used a human mast cell line, HMC-1, to determine if mast cells can induce normal human dermal fibroblasts to differentiate into functional myofibroblasts in vitro. We monitored the differentiation process by assaying two properties of the myofibroblast phenotype: expression of alpha-smooth muscle actin and functional capacity to contract a collagen matrix. In both a simple coculture system and in a skin-equivalent culture system, HMC-1 cells induced alpha-smooth muscle actin expression by fibroblasts. HMC-1 cells also stimulated fibroblast contraction of collagen gels, and the relative amount of contraction was dependent upon the number of HMC-1 cells present. To characterize the individual contributions made by specific mast cell products, we examined the effects of histamine, tumor necrosis factor alpha, and tryptase. Histamine induced a clear increase in alpha-smooth muscle actin expression, but it did not appear to stimulate fibroblast contraction. Tumor necrosis factor alpha had no effect in either assay. Purified human tryptase induced alpha-smooth muscle actin expression, and blocking the proteolytic activity of tryptase with specific inhibitors reduced that response. Tryptase inhibitors also eliminated the ability of HMC-1 cells to stimulate fibroblast contraction, suggesting that tryptase secreted by the HMC-1 cells may be one of the active mast cell mediators.

The role of the immune system in conjunctival wound healing after glaucoma surgery

The immune system has a fundamental role in the development and regulation of ocular healing, which plays an important role in the pathogenesis of most blinding diseases. This review discusses the mechanisms of normal wound healing, describing the animal and fetal wound healing models used to provide further insight into normal wound repair. In particular, conjunctival wound repair after glaucoma filtration surgery will be used to illustrate the contributions that the different components of the immune system make to the healing process. The potential role of macrophages, the possible regulatory effect of lymphocytes, and the important role of growth factors and cytokines in the wound healing reaction are discussed. The significance of the immune system in the pathogenesis of aggressive conjunctival scarring is addressed, particularly assessing the predisposing factors, including drugs, age, and ethnicity. The rationale behind the pharmacological agents currently used to modulate the wound healing response and the effects these drugs have on the function of the immune system are described. Finally, potential new therapeutic approaches to regulating the wound healing response are reported.

Histamine effects on conjunctival fibroblasts from patients with vernal conjunctivitis

Histamine, an important mast cell mediator in allergic disorders, may affect extracellular matrix production and cell growth in vernal keratoconjunctivitis (VKC). In the present study, the histamine reactivity of conjunctival fibroblasts derived from VKC patients was investigated in vitro. Conjunctival fibroblast cultures were derived from biopses of 8 tarsal VKC patients and 5 normal subjects. These cells were maintained in vitro and stimulated with different concentrations of histamine with and without H1 (clorpheniramine) and H2 (cimetidine) receptor antagonists. Comparisons were made to fibroblasts grown in the same media without histamine and to fibroblasts stimulated with just antihistamine. The effects of histamine were evaluated by: (1) the MTT test to assess cell proliferation; (2) an in vitro wound model for cell migration and (3) the measurement of procollagen I (PIP) and procollagen III (PIIIP) in supernatants for collagen production. Results showed: (1) While VKC-derived fibroblasts proliferated at a faster rate than normal cells in unstimulated media, after histamine stimulation, VKC and normal cells grew at a similar rate. Both H1 and H2 antagonists significantly inhibited (P<0.05) histamine-induced cell proliferation. (2) Histamine enhanced cell migration after wounding; this effect was inhibited only by H2 antagonism. (3) When stimulated with histamine, VKC fibroblasts produced significantly more PIP than those in control media. Furthermore, VKC-derived fibroblasts were more sensitive to histamine challenge, producing significantly more PIP than normal fibroblasts. H1 and H2 antagonists did not modify histamine-stimulated PIP production. The enhanced proliferative and productive capacity of VKC fibroblasts may be the result of a selective overgrowth of one or more fibroblast subpopulations in a chronically inflamed tissue. Histamine increased proliferation, migration and collagen production in both normal and VKC fibroblasts. Since H2 antagonism modulated both cell growth and migration, but not histamine-induced collagen production, the latter may be mediated by a different receptor. These results showed that histamine is at least partially responsible for fibroblast stimulation.

Production of TNF-alpha by murine bone marrow derived mast cells activated by the bacterial fimbrial protein, FimH

Production of tumor necrosis factor alpha (TNF-alpha) by mast cells is an important aspect of host defense against gram negative bacteria. In order to define the intracellular pathways utilized by mast cells in this physiological, protective role, we have studied the production of TNF-alpha in bone marrow derived mast cells from the C3H/HeJ (LPS-insensitive) strain following exposure to bacteria expressing the fimbrial protein, FimH. Mast cells exposed to FimH produce TNF-alpha (300-1200 pg/10(6) cells) over 1-3 h compared with 1800-15,000 pg/10(6) cells produced by cells triggered via IgE/antigen. This low level of TNF-alpha production in vitro is compatible with the protective in vivo role of mast cells to produce modest amounts of TNF-alpha in contrast to the large amounts of mediators released during maximal activation. A second difference between the two signals is sensitivity to cyclosporin A (CsA). The IgE/antigen pathway is inhibited by 90-95% at 0.02 to 0.5 microM cyclosporin A whereas the FimH pathway is inhibited by only 40%. These data demonstrate that the intracellular pathway activated by FimH is different from that activated by IgE/antigen both in terms of amount of TNF-alpha produced and in sensitivity to CsA. This is the first evidence that FimH activates mast cells via a pathway that is distinct from that used by IgE/antigen.

Stem cell factor induction is associated with mast cell accumulation after canine myocardial ischemia and reperfusion

BACKGROUND

Myocardial infarction is associated with an intense inflammatory reaction leading to healing and scar formation. Because mast cells are a significant source of fibrogenic factors, we investigated mast cell accumulation and regulation of stem cell factor (SCF), a potent growth and tactic factor for mast cells, in the healing myocardium.

METHODS AND RESULTS

Using a canine model of myocardial ischemia and reperfusion, we demonstrated a striking increase of mast cell numbers during the healing phase of a myocardial infarction. Mast cell numbers started increasing after 72 hours of reperfusion, showing maximum accumulation in areas of collagen deposition (12.0+/-2.6-fold increase; P<0.01) and proliferating cell nuclear antigen (PCNA) expression. The majority of proliferating cells were identified as alpha-smooth muscle actin-positive myofibroblasts or factor VIII-positive endothelial cells. Mast cells did not appear to proliferate. Using a nuclease protection assay, we demonstrated induction of SCF mRNA within 72 hours of reperfusion. Immunohistochemical studies demonstrated that a subset of macrophages was the source of SCF immunoreactivity in the infarcted myocardium. SCF protein was not found in endothelial cells and myofibroblasts. Intravascular tryptase-positive, FITC-avidin-positive, CD11b-negative mast cell precursors were noted in the area of healing and in the cardiac lymph after 48 to 72 hours of reperfusion.

CONCLUSIONS

Mast cells increase in number in areas of collagen deposition and PCNA expression after myocardial ischemia. The data provide evidence of mast cell precursor infiltration into the areas of cellular injury. SCF is induced in a subset of macrophages infiltrating the healing myocardium. We suggest an important role for SCF in promoting chemotaxis and growth of mast cell precursors in the healing heart.